Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$243.50	12.591%	$274.1591	$274.16	$274.15	$274.20
Purchase #2	$5.71	12.131%	$6.4027	$6.40	$6.40	$6.40
Purchase #3	$180.66	8.154%	$195.391	$195.39	$195.40	$195.40
Purchase #4	$89.44	11.706%	$99.9098	$99.91	$99.90	$99.90
Purchase #5	$21.30	13.119%	$24.0943	$24.09	$24.10	$24.10
Purchase #6	$196.59	3.527%	$203.5237	$203.52	$203.50	$203.50
Purchase #7	$248.73	6.697%	$265.3874	$265.39	$265.40	$265.40
7 purchase totals =	$985.93		$1,068.8680	$1,068.86	$1,068.85	$1,068.90